No abstract

The barley HVA1 gene, encoding a member of the group 3 late embryogenesis abundant (LEA) proteins, has previously been introduced into spring wheat cv. Hi‐Line to determine its effect on drought tolerance (Sivamani E, Bahieldin A, Wraith JM, Al‐Niemi T, Dyer WE, Ho T‐HD, Qu R (2000) Improved biomass productivity and water use efficiency under water deficit conditions in transgenic wheat constitutively expressing the barley HVA1 gene. Plant Sci 155, 1–9). T4 progeny from six independent transgenic events (lines 111/1, 1/1, 11/2, 84, 765 and 1201) were tested in nine field experiments over six cropping seasons. In the first two seasons, the total biomass per plot and the grain yield per plot of line 111/1 were higher than those of line 1/1, and higher than those of the wild‐type control in the second season. The grain yield per plot of line 11/2 was significantly lower than that of the transgenic lines 111/1 and 1/1 in the third season, and this line was not tested further. In the fourth season, the plant height and grain yield per plot of line 111/1 were significantly higher than those of the wild‐type control. Under dryland conditions in the fifth season, line 111/1 showed significantly greater plant height, total biomass per plot and grain yield per plot than the wild‐type control in at least two of the four locations, as well as across locations. In the sixth season, newly developed transgenic lines 1201 and 765 significantly overyielded the two original transgenic lines 111/1 and 1/1, the non‐expressing transgenic line 84 as well as the wild‐type control in the three yield attributes and leaf water measurement, namely relative water content (RWC). This result coincided with the rate of HVA1 transgene expression of the different genotypes. Differences in total seed storage protein concentrations between the transgenic lines and the wild‐type control within or across environmental conditions were insignificant. These field trials show that the HVA1 gene has the potential to confer drought stress protection in transgenic spring wheat.

Diatoms are mostly photosynthetic eukaryotes within the heterokont lineage. Variable plastid genome sizes and extensive genome rearrangements have been observed across the diatom phylogeny, but little is known about plastid genome evolution within order- or family-level clades. The Thalassiosirales is one of the more comprehensively studied orders in terms of both genetics and morphology. Seven complete diatom plastid genomes are reported here including four Thalassiosirales: Thalassiosira weissflogii, Roundia cardiophora, Cyclotella sp. WC03_2, Cyclotella sp. L04_2, and three additional non-Thalassiosirales species Chaetoceros simplex, Cerataulina daemon, and Rhizosolenia imbricata. The sizes of the seven genomes vary from 116,459 to 129,498 bp, and their genomes are compact and lack introns. The larger size of the plastid genomes of Thalassiosirales compared to other diatoms is due primarily to expansion of the inverted repeat. Gene content within Thalassiosirales is more conserved compared to other diatom lineages. Gene order within Thalassiosirales is highly conserved except for the extensive genome rearrangement in Thalassiosira oceanica. Cyclotella nana, Thalassiosira weissflogii and Roundia cardiophora share an identical gene order, which is inferred to be the ancestral order for the Thalassiosirales, differing from that of the other two Cyclotella species by a single inversion. The genes ilvB and ilvH are missing in all six diatom plastid genomes except for Cerataulina daemon, suggesting an independent gain of these genes in this species. The acpP1 gene is missing in all Thalassiosirales, suggesting that its loss may be a synapomorphy for the order and this gene may have been functionally transferred to the nucleus. Three genes involved in photosynthesis, psaE, psaI, psaM, are missing in Rhizosolenia imbricata, which represents the first documented instance of the loss of photosynthetic genes in diatom plastid genomes.

Heat stress threatens agriculture worldwide. Plants acquire heat stress tolerance through priming, which establishes stress memory during mild or severe transient heat stress. Such induced thermotolerance restructures metabolic networks and helps maintain metabolic homeostasis under heat stress. Here, we used an electrospray ionization mass spectrometry-based platform to explore the composition and dynamics of the metabolome of Arabidopsis thaliana under heat stress and identify metabolites involved in thermopriming. Primed plants performed better than non-primed plants under severe heat stress due to altered energy pathways and increased production of branched-chain amino acids, raffinose family oligosaccharides (RFOs), lipolysis products, and tocopherols. These metabolites serve as osmolytes, antioxidants and growth precursors to help plants recover from heat stress, while lipid metabolites help protect membranes against heat stress. The carbohydrate (e.g., sucrose and RFOs) and lipid superpathway metabolites showed the most significant increases. Under heat stress, there appears to be crosstalk between carbohydrate metabolism (i.e., the thermomemory metabolites stachyose, galactinol, and raffinose) and tyrosine metabolism towards the production of the thermomemory metabolite salidroside, a phenylethanoid glycoside. Crosstalk occurs between two glycerophospholipid pathways (the biosynthetic pathways of the thermomemory metabolite S-adenosyl-L-homocysteine and the terpenoid backbone) and the δ-tocopherol (chloroplast lipid) pathway, which favors the production of glycine betaine and other essential tocopherols, respectively, compounds which are essential for abiotic stress tolerance in plants. Therefore, metabolomic analysis can provide comprehensive insights into the metabolites involved in stress responses, which could facilitate plant breeding to maximize crop yields under adverse conditions.